icd/common/icd-utils.c

/*
 * Vulkan
 *
 * Copyright (C) 2014 LunarG, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 * Authors:
 *    Chia-I Wu <olv@lunarg.com>
 */

#include "icd-utils.h"

/* stolen from Mesa */
uint16_t u_float_to_half(float f)
{
    union fi {
        float f;
        uint32_t ui;
    };

   uint32_t sign_mask  = 0x80000000;
   uint32_t round_mask = ~0xfff;
   uint32_t f32inf = 0xff << 23;
   uint32_t f16inf = 0x1f << 23;
   uint32_t sign;
   union fi magic;
   union fi f32;
   uint16_t f16;

   magic.ui = 0xf << 23;

   f32.f = f;

   /* Sign */
   sign = f32.ui & sign_mask;
   f32.ui ^= sign;

   if (f32.ui == f32inf) {
      /* Inf */
      f16 = 0x7c00;
   } else if (f32.ui > f32inf) {
      /* NaN */
      f16 = 0x7e00;
   } else {
      /* Number */
      f32.ui &= round_mask;
      f32.f  *= magic.f;
      f32.ui -= round_mask;

      /*
       * Clamp to max finite value if overflowed.
       * OpenGL has completely undefined rounding behavior for float to
       * half-float conversions, and this matches what is mandated for float
       * to fp11/fp10, which recommend round-to-nearest-finite too.
       * (d3d10 is deeply unhappy about flushing such values to infinity, and
       * while it also mandates round-to-zero it doesn't care nearly as much
       * about that.)
       */
      if (f32.ui > f16inf)
         f32.ui = f16inf - 1;

      f16 = f32.ui >> 13;
   }

   /* Sign */
   f16 |= sign >> 16;

   return f16;
}